The present invention relates to a method and device for feeding powderized raw material, such as aluminum oxide, into an electrolyte melt in which aluminum electrolysis occurs, and in which a reciprocatingly vibrating feeding means is used.
The invention is classified within the electrolytic production range of aluminum, and it can be used for feeding aluminum oxide and other equivalent materials into all kinds of electrolysis processes.
In prior art methods and devices, the aluminum electrolysis process is accomplished as a continuous process with a raw material being fed into the electrolysis process usually intermittently at given time intervals. Typically, the feeding takes place by penetrating the crust of an electrolysis and by carrying an uncontrolled portion of aluminum oxide into an electrolyte melt, which prior to penetration had been spread upon the crust.
In connection with such prior art methods, major failures and drawbacks occur which cause instability in the electrolysis process. This is primarily due to the fact that the aluminum oxide concentration in the electrolyte melt, in which electrolysis occurs, changes from the maximum value of the charging moment to a minimum value of the starting phase of an anode effect. As a result, the consumption of electrical energy increases and the efficiency of the process decreases, causing precipitation on the bottom of the electrolyte melt. This precipitation has the significant drawback of causing disturbances in the activity of the electrolysis.
Another current significant problem in electrolytic aluminum production by means of the prior art devices is to guarantee a reliable and simple continuous feeding of the raw material in the electrolysis without increasing the breaking of the crust of the electrolyte so that a sufficiently uniform aluminum oxide concentration can be maintained in the electrolysis.
In the prior art, U.S. Pat. No. 2,713,024 describes a method for continuously feeding aluminum electrolysis wherein aluminum oxide is fed continuously under the molten surface with the aid of a feeding means in a pipe positioned on the surface of electrolyte melt. The aluminum oxide is carried in the form of an aluminum oxide column formed in the inlet point into the electrolyte melt with pressure provided with the feeding means. A particular feature of the method described in this patent is that the feeding means which produce the feeding pressure of the aluminum oxide column is not in contact with the electrolyte melt. The feeding process described in this U.S. patent can be used, irrespective of the anode melt, in an electrolysis of any power. In addition, the process is carried out with a screw, piston, or an equivalent type feeding means.
In spite of certain advantages of the above-mentioned U.S. patent, it has not achieved wide-spread use because at the point in which raw material is taken through the electrolyte crust into the electrolyte melt, large forces are created as a result of the rapid growth of the inlet point.
An aluminum oxide feeding method for aluminum electrolysis is also known in the prior art from U.S.S.R. Inventor's Certificate No. SU 126 271. This reference describes the feeding of aluminum oxide into an electrolytic process using a vibration method in order to accelerate the dissolution of aluminum oxide in the electrolyte melt and to prevent precipitation on the bottom of the electrolyte melt. The method described by this U.S.S.R. Inventor's Certificate is implemented by using a spherical tank provided with holes, which is immersed in the electrolyte melt and vibrated horizontally. The aluminum oxide in the spherical tank is under the influence of vibration and dissolves in the electrolyte melt. According to another alternative embodiment of this reference, the implementation of the method is carried out with a horizontal, vibrating plate, in which the amplitude of vibration is directed horizontally. This prior art method is not applied in practice because maintaining the surface of the molten electrolyte open in the aluminum oxide feeding point is difficult because a crust is produced rapidly on the surface of the electrolyte when cold aluminum oxide enters into contact with the electrolyte melt.
In addition, with regard to the prior art, reference is made to the following patents: U.S.S.R. Inventor's Certificate No. SU 1,191,491, U.S. Pat. No. 5,045,168, and Great Britain Patent Application No. 2,058,137.